1. Field Of The Invention
This invention relates to a method of producing an extrusion having a wood grain appearance and an associated apparatus.
2. Background Information
It is well known to make extrusions using a screw feed extruder A standard screw feed extruder consists of (i) a cylindrical housing in which a screw is mounted for rotation about its longitudinal axis; (ii) a die and (iii) a puller section. In use, a pelletized or powderized plastic material, such as vinyl, is fed into the screw at one end thereof and is advanced through the housing by the action of the rotating screw. As the plastic material is advanced through the housing it is heated so as to melt the vinyl pellets or powder. The molten vinyl flows through the die to form the shape of the extrusion. The extruded product is pulled by the pulling section through the die to form the elongated extruded product. The elongated extruded product is then cut to desired lengths. See, e.g., U.S. Pat. Nos. 3,482,006; 4,054,403; 4,173,445; 4,252,755; and 4,859,068.
It is also known to produce extrusions having a marbled finish. U.S. Pat. No. 4,921,414 discloses an extrusion apparatus used to make a thermoplastic extrusion having a marbled appearance. That apparatus consists of a main screw feed extruder having an injection cavity and an injection device which is adjacent the injection cavity. The main extruder feeds in the base material into the injection cavity and the marbling material is injected into the injection cavity. These materials are mixed and the mixed materials are extruded through the die.
It is also known to provide different color sections on a main extrusion. This is accomplished by using a portable feed screw satellite extruder such as Model No. VT-1250-20 made by the Entwistle Company of Hudson, Mass. that operates in association with a main extruder. The satellite extruder consists of a housing in which a screw feed means is mounted and a hopper with a feed section. The hopper and feed section holds and feeds into the housing the different color material to be bonded onto the main extrusion made by the main extruder. The housing and the hopper and feed section are slidably mounted on a pole which in turn is connected at its lower section to a base having wheels. The satellite extruder, therefore, is portable and can be adjusted for different heights. The satellite extruder is wheeled to the main extruder and is connected thereto by means of a pipe that extends from the die of the main extruder to the housing of the satellite extruder. The material in the satellite extruder is introduced into the hopper and fed into the housing through the feed section. The screw feed means advances the material through the housing while at the same time melting the material so that it will flow into the die. The melted material then flows through the pipe and into an opening in the die at the same time the main extrusion is being extruded through the die. The second material will flow over the sections of the main extrusion which are desired to be a different color and will bond to the main extrusion. This will produce an extrusion having a section which has a different color than the remainder of the extrusion.
As extrusions are widely used for building products, design considerations sometimes dictate providing a wood grain appearance for a section of the extrusion. For example, a vinyl extrusion might be used for a window frame where it is desired to have an interior section having a wood grain appearance with the remainder of the extrusion being white in color. In this case, the second material which is fed into the second extruder is comprised of a mixture of several colors of pellets or multi-colored powder such as brown, black and white in order to obtain a wood grain finish. This mixture of pellets or powder is fed into the screw feed means and is melted together so that it will flow through the pipe and into the die. A problem has arisen, however, in creating the wood grain appearance. The problem is that the melted pellets mix too quickly, thus forming a solid color on the extrusion instead of a wood grain appearance. The solid color does not look like a wood grain and thus does not meet the design and aesthetic characteristics desired by the maker of the building product.
Therefore, there remains a need for a method to make an extrusion having a wood grain finish and an associated apparatus.